Table 1

Characteristics of the different patient groups studied with juvenile idiopathic arthritis and related disorders

Characteristics

PP+ (n = 45)

PP- (n = 96)

CO (n = 55)

PP+ versus PP-

PP+ versus CO

Female (%)

76

65

58

Mean age (years)

4.7

8.2

8.6

P < 0.01^a

P < 0.01^a

Laboratory findings

Haemoglobin level <11.8 g/dl (%)

61

34

24

P < 0.01^b

P < 0.01^b

Mean white blood cell count (cells/μl)

10,440

8,000

8,110

P < 0.01^a

P < 0.01^a

Mean platelet count (×10e³/μl)

409

362

332

P < 0.01^a

ESR >11 mm/hour (%)

71

51

30

P < 0.01^c

P < 0.01^c

Positivity for ANAs (%)

51

45

24

P < 0.05^b

Factors relating to the skin

SPT I and II (%)

58

39

53

P < 0.05^b

Freckles (%)

42

34

36

Blue/grey eye colour (%)

68

72

60

Fair hair colour (%)

61

50

51

Regular skin care (%)

82

75

82

Intense sun exposure during vacation (%)

47

31

25

P < 0.05^b

Photoprotective measures (%)

89

83

85

Application of sun screen with >20 SPF (%)

44

50

42

Atopic diathesis (%)

21

25

16

Psoriasis (%)

8

3

2

Factors relating to naproxen therapy and comedication

Mean duration of naproxen therapy (months)

22.8

20.2

-

Mean dosage of naproxen (mg/kg per day)

16.7

15.5

-

Maximal mean dosage of naproxen (mg/kg per day)

17.6

16.7

-

Increased naproxen dosage during the course of treatment (%)

42

24

-

P < 0.05^b

Comedication (%)

58

38

-

P < 0.05^b

Chloroquine as comedication (%)

27

6

-

P < 0.01^b

^aMann-Whitney U-test. ^bχ² test. ^ct-test for independent samples. ANA, antinuclear antibody; CO, children not treated with naproxen (controls); ESR, erythrocyte sedimentation rate; PP+, children treated with naproxen who developed pseudoporphyria; PP-, children treated with naproxen who did not develop pseudoporphyria; SPF, sun protection factor; SPT, skin phototype.

Schäd et al. Arthritis Research & Therapy 2007 9:R10   doi:10.1186/ar2117